In this case a software decoder needs decode to a higher sample rate (e.g. 2x) for the transient filter to work.

Quote from: Replica9000 on 2024-08-30 22:59:49

Looks like I can make a 20-bit file with SoX.

Code: [Select]

sox input_hdcd.flac -b 24 output_20b.flac dither -p 20

This means dither to 20 bits, because SoX uses a traditional approach (contrast to e.g. Case's smart dither), the LSBs will always be filled, even when the input is digital silence (all zero).

sox 24bit.flac 17bit.flac" -D vol 3.0517578125e-5 vol 32768 stats
sox 24bit.flac 18bit.flac" -D vol 6.103515625e-5 vol 16384 stats
sox 24bit.flac 19bit.flac" -D vol 1.220703125e-4 vol 8192 stats
sox 24bit.flac 20bit.flac" -D vol 2.44140625e-4 vol 4096 stats
sox 24bit.flac 21bit.flac" -D vol 4.8828125e-4 vol 2048 stats
sox 24bit.flac 22bit.flac" -D vol 9.765625e-4 vol 1024 stats
sox 24bit.flac 23bit.flac" -D vol 1.953125e-3 vol 512 stats

The data signal then goes to delay module  222, which gives the control decode module 221 time to figure out what to do with the signal before it gets to the first DSP subsystem 223. The first DSP module 223 is the complement to module 210 in the encoder. It does a peak expansion which restores the peaks limited in 210. It does a low level gain expansion, restoring the low level dynamics compressed in 210. It can complement the low level forcing of high frequencies in the dynamic dither operation, restoring a flat frequency response and lowering quantization noise. It performs some house keeping functions, and its signal output has 18 to 20 bits of real information at the one-times sampling rate (44.1 kHz for CD).

This more accurate digital signal at the media sampling rate is routed to the second digital signal processor sub system 224, which is complementary to encode module 205. In this subsystem, the signal is interpolated to a higher sampling rate using a variety of smoothing filters which are chosen to complement the decimation filters in 205.

I imagine that HDCD capable CD players and DACs also automatically apply a ReplayGain of sorts to compensate for that same HDCD decoded 'loss', at least that's what my Pacific Microsonics equipped CD player seems to do with HDCDs

I imagine that HDCD capable CD players and DACs also automatically apply a ReplayGain of sorts to compensate for that same HDCD decoded 'loss', at least that's what my Pacific Microsonics equipped CD player seems to do with HDCDs.

The commands below truncate any 24-bit input file to 17-23 bits without dither. Try to compare file size between HDCD decodes and normal 24-bit files. -D disables automatic dither. SoX by default applies no dither if output bit-depth >= 24, but IIRC a 3rd party compile I used still dither with 24-bit output.

Code: [Select]

sox 24bit.flac 17bit.flac" -D vol 3.0517578125e-5 vol 32768 stats
sox 24bit.flac 18bit.flac" -D vol 6.103515625e-5 vol 16384 stats
sox 24bit.flac 19bit.flac" -D vol 1.220703125e-4 vol 8192 stats
sox 24bit.flac 20bit.flac" -D vol 2.44140625e-4 vol 4096 stats
sox 24bit.flac 21bit.flac" -D vol 4.8828125e-4 vol 2048 stats
sox 24bit.flac 22bit.flac" -D vol 9.765625e-4 vol 1024 stats
sox 24bit.flac 23bit.flac" -D vol 1.953125e-3 vol 512 stats

Quote from: bennetng on 2024-11-24 15:57:33

Quote from: Porcus on 2024-11-24 11:29:37

That said, the 20 bits could have come from the advertising bragging.

From hardware perspective, 20-bit could have been chosen due to availability/cost/performance concern 20-30 years ago.

The Pacific handled 24 bits. HDCD encoding was part of the downmix from 88.2/24 to 44.1/16.
It also handled 20 bits, though.

THD+N of -74dB, DR of 74dBA. Not great. Good size spikes at 60Hz and 180Hz and that's with an upgraded power supply (PS-2). Harmonics are fairly high in level, and seem to not go down by much with increasing frequency. That's bad.

I wanted to see a visual of what the different is between the original audio and the audio after decoding with the HDCD filter.  The filter lowers the gain by -6dBFS, and outputs to 24-bit WAV.  I used ffmpeg to apply the filter, and to draw the waveforms.  The waveforms are the original audio (orange, lowered by 6dBFS) over the decoded waveform (light orange).

This is the track "Blue Monday" that does use Peak Extend.

ffmpeg -i blue_monday_orig.wav -lavfi showwavespic=split_channels=1:filter=peak:s=1600x800:colors="#E17400" blue_monday_orig.png
ffmpeg -i blue_monday_orig.wav -af hdcd -c:a pcm_s24le blue_monday_hdcd.wav
ffmpeg -i blue_monday_hdcd.wav -lavfi showwavespic=split_channels=1:filter=peak:s=1600x800:colors="#E17400" blue_monday_hdcd.png